Plastisol ink for textiles

ABSTRACT

The present invention relates to a plastisol ink for textiles and in particular to a screen printable PVC/phthalate-free plastisol textile ink having good storage stability and excellent wet-on-wet printing. characteristics. The plastisol textile ink of the present invention is substantially free of PVC and phthalates and comprises (i) a core-shell acrylic polymer having an acrylic polymer shell with a T g  of 90-125° C. and an acrylic polymer core with a lower T g  than the shell, (ii) an organic phosphate plasticiser having a viscosity of 60-120 mm 2 /s, and (iii) a pigment. Any particulate components in the ink have a particle size of 1-80 μm.

The present invention relates to a plastisol ink for textiles and inparticular to a screen printable PVC/phthalate-free plastisol textileink having good storage stability and excellent wet-on-wet printingcharacteristics.

A plastisol is a dispersion of fine polymer particles in a liquidplasticiser. Other components are added according to necessity, such aspigment, fillers, thixotropic agents, blowing agents, stabiliser etc.Under ambient storage conditions the polymer does not dissolve to anyextent in the plasticiser, but on heating to temperatures typicallyabove 100° C. the plastisol composition gels to form a homogenouscoalesced mass that retains its gelled form on cooling.

Plastisols are typically used in coatings, such as sealants and cableinsulation, and for textiles. Historically, polyvinyl chloride (PVC) hasbeen found to be the most suitable polymer for plastisol compositions.However, PVC has the disadvantage that hydrochloric acid is generated onburning, which can lead to toxic by-products on waste disposal byincineration and consequently is not a desirable material from the pointof view of health, safety and environmental protection. The most commonplasticisers are alkyl phthalates. However, several low-cost phthalateplasticisers are now thought to act as endocrine disruptors and henceare also becoming undesirable in textile applications.

Thus, there is a requirement for a plastisol ink for screen printingtextiles with the same stability, processing and finished printcharacteristics as a PVC/phthalate plastisol, but without the associatedhealth, safety and environmental problems.

The particular requirements for a plastisol screen printing ink fortextiles include being capable of pigmentation, having a stableviscosity, being suitable for storage for several years, beingoverprintable without pre-drying, i.e. being wet-on-wet printablewithout offsetting between the prints, and being capable of coalescingat bake temperatures of typically 130-160° C. for 2-5 minutes. Thefinished print must have acceptable cosmetic features, such as goodhandle and adhesion to the textile substrate even after washing. Theability to print wet-on-wet is particularly advantageous for acommercial product as it enables the printer to print continuouslywithout having to stop and clean the screen to avoid offsetting the ink.

PVC free plastisols have been proposed for use as screen printing inks,see WO 98/29507. However, the PVC/phthalate-free plastisols described inthe prior art are not of comparable quality to commercial PVC-typeplastisol inks.

Accordingly, the present invention provides a plastisol textile inkwhich is substantially free of PVC and phthalates comprising

-   -   (i) a core-shell acrylic polymer having an acrylic polymer shell        with a T_(g) of 90-125° C. and an acrylic polymer core with a        lower T_(g) than the shell,    -   (ii) an organic phosphate plasticiser having a viscosity of        60-120 mm²/s, and    -   (iii) a pigment,        wherein any particulate components in the ink have a particle        size of 1-80 μm.

Preferably the acrylic polymer shell has a T_(g) of 100-110° C.

Preferably the core-shell polymer has a particle size of 5-20 μm.

Preferably the organic phosphate plasticiser has a viscosity of 90-110mm²/s.

Preferably the organic phosphate plasticiser is an aryl phosphate,particularly preferably trixylyl phosphate.

Preferably the ratio of the core-shell polymer (i) to the totalplasticiser content (ii) is from 1:1 to 1:3 by weight, particularlypreferably from 1:1.2 to 1:2 by weight.

Preferably the plastisol textile ink is suitable for high definitionwet-on-wet printing through meshes up to 120 threads per cm PW (plainweave).

Preferably the plastisol textile ink further comprises a thermoplasticpolymer, which is preferably a polyester hot melt powder.

Preferably the plastisol textile ink further comprises a blowing agent.

Preferably the plastisol textile ink further comprises a flameretardant.

The present invention also provides the use of an ink as defined abovefor screen printing.

Plastisols comprising a polymer of alkyl methacrylate and an esterplasticiser are known (see GB 1516510). This type of plastisol has beenfurther improved by using an acrylate having a core-shell construction,where the core material is compatible with the plasticiser and the shellmaterial is incompatible with the plasticiser (see GB 1,581,493). Theouter shell is therefore resistant to the plasticiser at ambienttemperatures, but may be penetrated by the plasticiser at elevatedtemperatures, which then allows easy solubilisation due to thecompatible inner core, i.e. the core material alone would gel with theplasticisers even at room temperature within a short time, however, instorage, the shell material provides sufficient protection againstpremature gelling of the core material.

Any acrylate-based core-shell polymer having the required physicalproperties may be used in the ink of the present invention.Specifically, the shell of the core-shell polymer is incompatible withthe plasticiser and has a glass transition temperature (T_(g)) of90-125° C. The term “incompatible” is understood in the art to meanresistant to the plasticiser at ambient temperatures (20-25° C.). Thecore has a lower T_(g) than shell and is compatible with the platiciser.Again, “compatible” is a term of the art and indicates that the core ispenetratable by the plasticiser at elevated temperatures, i.e. higherthan ambient temperatures, to form a gel.

Such core-shell polymers are well known in the art and are commerciallyavailable. By way of example, the core-shell polymer may be a core-shellpolymer consisting of (a) a core material compatible with theplasticiser and comprising a polymer derived from a monomer or monomercomposition comprising (i) 15 to 100% by weight of at least one of C₃₋₂₅alkyl acrylates and C₂₋₂₅ alkyl methacrylates, and optionally styrene;(ii) 0 to 85% by weight of at least one monomer selected from methylacrylate, methyl methacrylate and ethyl acrylate; and/or (iii) 0 to 20%by weight of one or more further radically polymerisable monomers; and(b) a shell material which is incompatible with the plasticiser, theshell material comprising a homopolymer of methyl methacrylate or acopolymer containing at least 80% by weight of units of methylmethacrylate and having a glass temperature of 90-125° C., the corematerial (a) and the shell material (b) being present in a weight ratioof 3:1 to 1:3.

The preparation of core-shell polymers of this type is well-known in theart, see, for example, GB 1,581,493. In one process, the core-shellpolymer is prepared by emulsion polymerisation. The monomers forming thecore material are polymerised in aqueous emulsion in a first processstep. When the monomers of the first step are substantially polymerised,the monomers forming the shell material are added to the emulsionpolymer under such conditions that the formation of new particles isavoided. The polymer obtained in the second step is deposited in theform of a shell around the core material. A favourable ratio of shellthickness to core size is obtained if the weight of core material toshell material is 1:3 to 3:1. The dispersions are obtained may beconverted into a dry powder by drying in conventional manner.

In the plastisol, the individual. core-shell polymer particles aggregateto form larger particles. These aggregate particles must have a particlesize of 1-80 μm, preferably, 5-50 μm, particularly preferably 5-20 μm.Aggregate particle sizes may be determined by optical or physicalseparation methods. The term “particle size” used herein represents anaverage particle diameter, i.e. V₅₀.

Any phosphate plasticiser may be used in the present invention providedit has a viscosity of 60-120mm²/s. However, tri(C₁₋₆-substituted phenyl)phosphates are preferred. Particularly preferred phosphates includeisopropylated triaryl phosphate, tricresyl phosphate, (phenyl,isopropoxylate phosphate 3/1) and trixylyl phosphate.

The viscosity of the plasticiser is measured at 25° C. using a CAP2000Cone and Plate viscometer fitted with a no. 4 cone at 100 rpm.

The plastisol is substantially free of PVC and phthalates. The term“substantially free” here means that the amount of PVC is sufficientlylow so as not to require removal of hydrochloric acid on incinerationand the amount of phthalate is below toxic levels. Preferably PVC ispresent at less than 1% and phthalate is present at less than 1%.

The pigment must be compatible with the other components in the ink andmust not interfere with plastisol formation, but otherwise any pigmentis acceptable. A large number of pigments are commercially available andare well known to the skilled person. The pigment must have a particlesize of 1-80 μm, preferably, 5-50 μm, particularly preferably 5-20 μm.

The plastisol ink of the present invention should have a viscosity of1-10 Pas (10-100 poise). When used as an ink, the plastisol ink shouldpreferably have a viscosity of 3-4 Pas (30-40 poise). When used as abase coat, the plastisol ink should preferably have a viscosity of 5-6Pas (50-60 poise). The viscosity of the plastisol ink may be varied byvarying the ratio of core-shell polymer to plasticiser. The ink shouldalso have a wide latitude of cure, i.e. from 110 to 200° C., to form aflexible and durable coating on the garment which is resistant towashing at 60° C. The ink is also capable of being pigmented to give arange of colours from which a Pantone® system can be matched and may beopaque in colour so as to be suitable for use on light or darksubstrates.

The plastisol ink of the present invention may also contain optionaladditives, well known in the art, which would be normally be used tomodify PVC/phthalate plastisols to give other decorative effects or thealter the theological properties of the ink.

One example is to generate swelling on curing to produce a “Puff”effect. These additives, known in the art as blowing agents, aretypically chemicals which breakdown on heating to give gaseousbyproducts, such as Expancel® 461 DU Microsphere (supplied by Expancel),Unicell OH (supplied by OMYA), and Genitron LE (supplied by Acrol) orgas-encapsulated thermoplastic microspheres.

If it is necessary to modify the rheology of the ink, before curing,then non-phosphate and non-phthalate plasticisers may be added to themixture. Preferably, polymeric plasticisers are blended with the(non-polymeric) organic phosphates. Polymeric plasticisers are wellknown in the art.

It is also known in the art that textile plastisol inks may be used asthermal transfer media, where the plastisol is printed first onto acarrier sheet, e.g. siliconised paper, and then partially heat hardened.At a later date, the ink layer may be transferred to a textile at ahigher temperature in a heated press. To facilitate the use as atransfer medium, additives such as thermoplastic polymers, which areinsoluble in the plastisol, may be incorporated by simply dispersing thethermoplastic polymer into the plastisol by a mixing process. Examplesof thermoplastic polymers are Schaetti Fix 374 (Polyester Hotmelt powdersupplied by Bostik), Griltex 1AP1 and Griltex 2AP1 (Polyamide Hotmeltpowders supplied by EMS).

EXAMPLES Examples 1-21

The table below illustrates the importance of selecting the correctcombination of T_(g) of the acrylic with the plasticiser to obtain therequired properties of compatibility and stability.

The acrylic and plasticiser were made in the proportions of 1:1.5. Acommercial plastisol textile, i.e. Texopaque® OP381 (Sericol Ltd) wasused as the PVC/phthalate formula type control.

The terms “compatibility” and “stability” used in the table below havethe following meanings.

Compatibility: Apply a layer of the acrylic/plasticiser mixture onto aglass plate and heat in an oven at 160° C. for 3 min. Allow to cool andobserve the degree of separation of the plasticiser over several days.The separated plasticiser is clearly distinguishable as a clear liquidand is distinct from the more opaque solid plastisol mixture. Good meansno migration of the plasticiser after 14 days further at roomtemperature. Moderate means some separation within 1-14 days. Poor meansseparation in less than 24 hrs.

Stability: The acrylic/plasticiser mixture is stored in a sealed pot at40° C. over 4 weeks. There should be no substantial increase inviscosity during this test, which simulates several years storage atambient temperatures. Good means no gelling after 4 weeks. Moderatemeans gelled in 1 day-4 weeks. Poor means gelled in less than 24 hrs.Plasticiser T_(g) of Viscosity at Example acrylic 25° C. PlastisolPlastisol No. (° C.) Plasticiser (mm²/s) Compatibility Stability  1* PVCControl Good Good  2* 85 trixylyl phosphate 110 Moderate Poor  3 90trixylyl phosphate 110 Moderate Moderate  4 95 trixylyl phosphate 110Moderate Good  5* 110 2-ethylhexyl 22 Good Poor diphenyl phosphate  6*110 isodecyl diphenyl 22 Good Poor phosphate  7* 110 C₁₂-C₁₆ alkyl 24Good Poor diphenyl phosphate  8* 110 cresyl diphenyl 31 Good Poorphosphate  9 110 isopropylated 60 Good Moderate triaryl phosphate 10 110tricresyl 70 Good Moderate phosphate 11 110 phenyl, 93 Good Moderateisopropoxylate phosphate 3/1 12 110 trixylyl phosphate 110 Good Good 13114 trixylyl phosphate 110 Moderate/Good Good 14 118 isopropylated 60Good Moderate triaryl phosphate 15 118 tricresyl 70 Good Moderatephosphate 16 118 phenyl, 93 Moderate/ Good isopropoxylate Good phosphate3/1 17 118 trixylyl phosphate 110 Moderate Good 18 124 isopropylated 60Good Moderate triaryl phosphate 19 124 tricresyl 70 Good Moderatephosphate 20 124 phenyl, 93 Good Moderate/ isopropoxylate Good phosphate3/1 21 124 trixylyl phosphate 110 Moderate Good*indicates a comparative example which does not fall within the scope ofthe present invention.

Example 22 Example 23

Examples 22 and 23 were prepared using a standard high-speed stirrer toillustrate the importance of particle size of the acrylic resinselected. Example 22 Example 23 Core/shell acrylic particle size 50 μm20 — (T_(g) 110° C.) A Core/shell acrylic particle size <20 μm — 20(T_(g) 110° C.) Trixylyl phosphate 45 45 Kronos 2190 (Stirrable TiO₂pigment) 30 30

Examples 22 and 23 were printed under production conditions on a textilemulticolour screen printing machine. Example 22 allowed wet-on-wetprinting. Example 23 also allowed wet-on-wet printing but required lesscleaning than Example 22 (required no cleaning even after a thousandprints). Also Example 23 could more easily produce fine detail printsthan Example 22.

Examples 24-26

The following examples illustrate another embodiment of the presentinvention, where different coloured inks can be satisfactorily printedonto each other wet-on-wet without inter-colour drying. Example 24Example 25 Example 26 Core/shell acrylic of 20 38 36 T_(g) 110° C.(Particle size <20 μm) Trixylyl phosphate 45 60 58 TiO₂ pigment — 2 —Carbon black pigment — 2 — CI pigment red PR122 — — 2 Silica 0.5 — —Amine salt of 0.5 — — benzene sulfonic acid

These samples were printed using an M&R semi-automatic textile printingcarousel (Premiere) through silk screens of 120 threads per cm PW ontoblack cotton interlock. Example 24 was printed down first, followed by aflash cure schedule of 5 seconds at 500° C. (IR medium wavelengthoutput), this was then subsequently overprinted using screens containingthe ink of Example 25 followed by the ink of Example 26. These exampleswere printed wet-on-wet, without any significant picking of the ink whenoverprinted by subsequent colours. The printed interlock was thenremoved from the machine and cured at a setting of 400° C. (M&R 2 metreRadicure Drier) on a IR belt drier at a conveyor belt speed of 4m/minute. The process was repeated using a standard commercial PVC andphthalate ink, i.e. “Texopaque” (Sericol Ltd) plastisols FW755, OP001and OP165. The resulting decorations made with the invention showedcomparable properties of wash resistance, opacity, flexibility anddurability as those made with the commercial “Texopaque” (Sericol Ltd)ink. In addition to these properties, the PVC/phthalate-free decorationdisplayed both a greater resistance to ignition by direct application ofa flame and a greater tendency to self-extinguish once alight whensubjected to industry standard methods for testing flammability.

The following example demonstrates the use of the invention as anexpanding “puff” ink.

Example 27

Core/shell acrylic of T_(g) 110° C. 25% Trixylyl phosphate 60% Gasencapsulated thermoplastic microspheres (Expancel 12% 461 microspheresfrom Boud Marketing Ltd) Fumed silica (Cab-o-sil TS530 from Cabot)  2%Amine salt of benzene sulfonic acid (Rhodacal A4D  1% from Caldic UKLtd)

The following example demonstrates the use of the invention as a thermaltransfer ink.

Example 28

Core/shell acrylic of T_(g) 110° C. 34% Trixylyl phosphate 50% Polyesterhot melt adhesive of mp 120° C. (Schaetti Fix 15% 374/0-80 from BostikLtd) Amine salt of benzene sulfonic acid(Rhodacal A4D from  1% Caldic UKLtd)

The following example demonstrates the use of the present invention withalternate physical printing characteristics using a blend of polymericand phosphate plasticisers.

Example 29

Core/shell acrylic of T_(g) 110° C. 46% Trixylyl phosphate 27% Polymericplasticiser 3-5 Pas (30-50 poise) at 25° C. 26% (Lankroflex PLA fromAkros Chemicals) Amine salt of benzene sulfonic acid (Rhodacal A4D  1%from Caldic UK Ltd)

1-14. (canceled)
 15. A plastisol textile ink which is substantially freeof PVC and phthalates comprising (i) a core-shell acrylic polymer havingan acrylic polymer shell with a T_(g) of 90-125° C. and an acrylicpolymer core with a lower T_(g) than the shell, (ii) an organicphosphate plasticiser having a viscosity of 60-120 mm²/s, and (iii) apigment, Wherein any particulate components in the ink have a particlesize of 1-80 μm.
 16. A plastisol textile ink as claimed in claim 15,wherein the acrylic polymer shell has a T_(g) of 100-110° C.
 17. Aplastisol textile ink as claimed in claim 15 wherein the core-shellpolymer has a particle size of 5-20 μm.
 18. A plastisol textile ink asclaimed in claim 1 wherein the organic phosphate plasticiser has aviscosity of 90-110 mm²/s.
 19. A plastisol textile ink as claimed inclaim 15, wherein the organic phosphate plasticiser is an arylphosphate.
 20. A plastisol textile ink as claimed in claim 19, whereinthe aryl phosphate plasticiser is trixylyl phosphate.
 21. A plastisoltextile ink as claimed in claim 15, wherein the ratio of the core-shellpolymer (i) to the total plasticiser content (ii) is from 1:1 to 1:3.22. A plastisol textile ink as claimed in claim 21, wherein the ratio isfrom 1:12 to 1:2.
 23. A plastisol textile ink as claimed in claim 15which is suitable for high definition wet-on-wet printing through meshesup to 120 threads per cm PW.
 24. A plastisol textile ink as claimed inclaim 15, further comprising a thermoplastic polymer.
 25. A plastisoltextile ink as claimed claim 24, wherein the thermoplastic polymer is apolyester hot melt powder.
 26. A plastisol textile ink as claimed inclaim 15, further comprising a blowing agent.
 27. A plastisol textileink as claimed in claim 15, further comprising a flame retardant.
 28. Ina method for screen printing wherein an ink is printed onto a substratethrough a screen, the improvement which comprises the ink being the inkof claim
 15. 29. In a method for screen printing wherein an ink isprinted onto a substrate through a screen, the improvement whichcomprises the ink being the ink of claim
 16. 30. In a method for screenprinting wherein an ink is printed onto a substrate through a screen,the improvement which comprises the ink being the ink of claim
 17. 31.In a method for screen printing wherein an ink is printed onto asubstrate through a screen, the improvement which comprises the inkbeing the ink of claim
 18. 32. In a method for screen printing whereinan ink is printed onto a substrate through a screen, the improvementwhich comprises the ink being the ink of claim
 19. 33. In a method forscreen printing wherein an ink is printed onto a substrate through ascreen, the improvement which comprises the ink being the ink of claim20.
 34. In a method for screen printing wherein an ink is printed onto asubstrate through a screen, the improvement which comprises the inkbeing the ink of claim 21.